Oxidized glutathione has an effect similar to that of glutathione reduced. As the effect that glutathione oxidized has, an effect such as detoxification in the liver by orally administration is known [J. Nutr. Sci. Vitaminol., Vol. 44, p. 613 (1998)]. Thus, glutathione oxidized can be used for various purposes for which glutathione reduced is used, and is, for example, useful as final products of, as raw materials for, or as intermediates of health foods, pharmaceuticals, cosmetics or the like.
As a process for producing glutathione oxidized, processes, such as a process for preparing a yeast extract thereof by concentration, dilution or the like of a glutathione oxidized solution which is obtained by oxidizing an aqueous solution, a yeast solution or the like of glutathione reduced obtained by a fermentation, an enzymatic preparation or the like, as a raw material, according to Japanese Published Unexamined Patent Application No. 146279/93, 177896/95 or the like; a process for preparing powders of a yeast extract containing glutathione oxidized by adding vehicles to the glutathione oxidized solution, and freeze-drying, spray-drying or the like; and a process for preparing powders (amorphous) of glutathione oxidized by separating and purifying the glutathione oxidized solution, and freeze-drying, spray-drying or the like, are known.
Since glutathione oxidized is difficult to obtain as crystals, glutathione oxidized in a solid form is supplied in the form of powders obtained by freeze-drying or the like (freeze-dried powders; amorphous). However, the freeze-drying is not suitable for industrial large-scale supply in its productivity. Accordingly, there exists a demand for crystals of glutathione oxidized and a process for production thereof which are suitable for large-scale supply or industrialization.
Furthermore, the freeze-dried powders of glutathione oxidized are known to have a problem in respect of stability because of their hygroscopicity, deliquescence, etc. Thus, they need to be refrigerated or frozen, or require special packaging to avoid moisture absorption when, for example, stored, transported or distributed. Accordingly, for its industrial large-scale supply, crystals of glutathione oxidized that can be stored at ordinary temperature and a process for production thereof are required.